DB2 will be responsible for generating a unique value for the column for each INSERT statement.

对于每条insert语句，DB 2将负责为其中的这一列生成一个惟一的值。

youdao

This guarantees that the column values remain unique and frees you from worrying about this column later on (don't try to assign a value to it, though).

这保证列值是惟一的并避免您为这个列操心(但是，不要尝试为它赋值)。

youdao

Without this requirement, the itemNumber column isn't guaranteed to be unique because multiple columns could be assigned a NULL value.

如果没有这个要求，itemnumber列就无法保持惟一，因为多个行都可能被分配null值。

youdao